The present invention is directed to electrical power supplies, and especially to direct currentxe2x80x94toxe2x80x94direct current (DC-DC) power supplies, also referred to as power converters, or converters. Prior art control of DC-DC power converters has largely been effected using analog control techniques and circuitry. Such analog approaches involve integrated circuits or discrete circuit elements, and require a product designer to select a priori a preferred control parameter or parameters. The designer thus needed to desensitize the product to anticipated ordinary variations in circuitry parameters caused by component tolerances and operating conditions during the process of optimizing the design. Designers employing such prior art control techniques thus had to predict the environment their product would encounterxe2x80x94such as, temperature values, electrical parameter values, and load values. Such pertinent parameters had to be estimated in order to choose control parameter values to be monitored and their acceptable variations, reactions to control parameter variances beyond predetermined limits, and to which parameters the circuitry must be desensitized for acceptable or optimal performance.
Digital control of converters has been implemented on a limited basis. At present, analog controls for converters remain faster and less expensive than digital controls. Nevertheless, digital control techniques and circuitry for DC-DC power converters have advantages in that they provide opportunities for real-time adjustment of operational and control parameters. A controller based on a microprocessor or a digital signal processor (DSP) offers a circuit designer access to adaptable control processes limited mainly by software execution speeds.
A direct design approach to optimizing efficiency of an operating DC-DC power converter using a digital controller (e.g., using a microprocessor or a DSP) would be to measure output power and input power, and to adjust various controllable parameters to maximize the power ratio. This approach is straightforward and logical because it measures the very parameters that make up the calculation for efficiency of a power supply: output power and input power. However, such a direct approach is complex and costly to construct and implement because of additional components required to accomplish the required measurements. Converters are commonly employed in products with the converter output voltage regulated to a specified value. Additionally, converters often have a substantially constant input voltage. With those two values presenting little variation during normal power supply operation, advantage can be taken of the duty cycle of the power train, which depends upon the ratio of the output voltage and the input voltage, remaining relatively constant, particularly for continuous current mode (CCM) operation. Duty cycle, as described below, presents an indicator for real-time optimization of the efficiency of the power train by adjusting controllable parameters.
There have been some attempts to adaptively operate power supply devices to improve efficiency. U.S. Pat. No. 5,742,491 of Apr. 21, 1998, to Bowman et al for xe2x80x9cPower Converter Adaptively Drivenxe2x80x9d, discloses a drive circuit for a power converter. The Bowman invention provides an apparatus and method for adjusting the timing for driving a power supply circuit with respect to the primary switch employed in the device. Variations of drive timing are achievable in response to varying operating conditions experienced by the power supply device. The Bowman invention is intended to maximize efficiency of the power supply while keeping stresses on individual components of the power supply within acceptable limits. According to Bowman, the optimum drive timing for one set of operating conditions is different from optimum drive timing for another set of operating conditions. As an example, a synchronous rectifier drive timing that produces maximum efficiency at a first load condition may produce excessive voltage stress on the rectifier switch at a second, lesser load condition. Conversely, when the timing is changed to lower the voltage stress at the second load condition, a loss of efficiency is liable to occur at the first load condition. Bowman""s apparatus and method provide for the designer an a priori adaptation of the delay between drive waveforms supplied to the inverter and synchronous rectifier of a power supply device as a function of an operating condition of the converter to allow the converter to operate efficiently in distinct operating environments over a range of operating conditions.
Bowman, therefore, succeeds in improving operation of a power supply device over a wider range of conditions. Bowman builds a representative test device and measures predetermined parameters associated with that test device in a laboratory environment. Bowman provides a delay circuit constructed for use in production devices as though the production devices will operate the same as the laboratory test devices that are the basis for Bowman""s determinations in designing the delay circuit. That is, Bowman""s does not provide dynamic real-time efficiency adjustment capability.
Prior art approaches to controlling DC-DC power converters during operation have relied upon fixed designs based upon engineering analysis or laboratory data to optimize efficiency for design-anticipated conditions. Some provisions for after-design adjustment of operating parameters have been attempted, but they have provided only coarse adjustment with less than ideal accommodation of changing conditions. There has been no facility for continuous realtime adjustment of parameters over a range to improve efficiency based upon real-time observation of extant parameters.
There is a need for an apparatus and method for providing fine adjustments of efficiency of a DC-DC power converter during normal operation to enable accommodation of varying operating conditions and device parameter variaton without adding significant cost or complexity to the converter design.
A method and apparatus or dynamically adjusting operation of a converter device to improve conversion efficiency is described. The converter device includes an inverter (and may include a synchronous rectifier) and is driven by a plurality of drive signals having a duty cycle. Each individual drive signal has a leading edge and a lagging edge. The method involves adjusting a controllable parameter and observing, or measuring, the duty cycle of a conversion device. In its preferred embodiment, the method comprises the steps of: (a) varying timing of a first drive signal a first amount; (b) observing the duty cycle of the conversion device; (c) further varying the first drive signal appropriately to alter the duty cycle toward an extremum; and (d) continuing to operate the converter device with the duty cycle proximate the extremum. In its most preferred embodiment, the method of the present invention includes the further step of: (e) periodically effecting steps (a)-(c) varying a drive signal other than the first drive signal. The apparatus of the present invention is an apparatus for dynamically altering operation of a converter device to improve conversion efficiency. The converter device includes an inverter and a synchronous rectifier (or, at least two actively controlled switches). The converter device is driven by a plurality of drive signals having a duty cycle. The apparatus comprises: (a) a drive varying means for varying timing of selected individual drive signals of the plurality of drive signals; and (b) a measuring means for measuring, or observing, the duty cycle. The measuring or observing means is connected with the drive varying means. In its most preferred embodiment, the apparatus of the present invention further comprises: (c) a control means for controlling the drive varying means. The control means is connected with the measuring or observing means and with the drive varying means, and effects the controlling to operate the converter device proximate an extremum for the duty cycle.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.